2022. augusztus 28., vasárnap

Function Generator Power Amplifier 1.

No. This is not the sane animal I wrote about in my last post. It is a different unit with a different function.

Ok. Start at the beginning.

I bought 47 Ronin unknown transformer. Wrote about it here: https://pakahuszar.blogspot.com/2022/04/new-arrivals-5.html

Started to play with those. Made some measurements:

It is clearly an SPMS transformer. It has 4:1 turn ratio (I guess it is from some kind of 48V supply. Maybe a PoE supply?), and ideally around 100kHz working frequency.
To test it further, I need to add some load to it.

And the problem starts here. My signal generator is not up to the task. So I need something for testing.

When I see such kind of requirement in front of me, I usually thinking further. I want something can be used for future tasks also.

It would be nice to have the following features:

  • Few tens of volts output (ideally 650Vpp - I'll be far from it, see later)
  • 5A maximum load on low voltages
  • DC - 1MHz bandwidth (100kHz was enough now, but for the later definitely i will need more)
  • Variable gain. Let see up to 40dB

 First, look around, what is available on the market:

Keysight 33502A (https://www.keysight.com/us/en/product/33502A/isolated-amplifier-2-channel-50-vpp.html)

Are you lost your mind? >$3500 for a bloody amplifier???

Rigol PA1011

Nice little fellow. Bit simple, but almost good enough. The ~$400 price tag, still too high

Siglent SPA1010

Same true what I wrote for the Rigol

Juntek DPA-2698

It is a real, born on Aliexpress unit. It has $89 price tag, what is acceptable. I'm just not happy with the 0.5A output power (it use two TI BUF634 diamond buffers - the diamond buffer will resurface later in this post)

Looked around on the DIY space. It looks like, this is not a widely required thing, so I only found two projects (the second one is based on the first, just added some extra circuitry on the PSU side)


The OPA541 would be a nice candidate, but at the end of the day, I didn't like this project, had problems with the bandwidth, etc.

Finally I decided to build/design something from starch. Actually found a circuit, in an application note. It is an operation amplifier extended with a diamond buffer designed by Jim Williams: https://www.analog.com/media/en/technical-documentation/application-notes/an47fa.pdf

The circuit in question on page 45-46 (Figure 101)

With changed semiconductor set and adjusted values, I intend to achieve 24Vpp output at 5A.

I run some simulations on it. Even with 40dB gain (two stage), I was able to easily achieve the targeted 1MHz bandwidth. I'm still not a real analog guy, so I don't yet know, if the whole concept will work. Here is the simulated (single stage) circuit with 0dB gain:

Added some digital control circuitry for it, and designed a PCB for it.

The control allows me to change the gain from 0 to 40dB in 5dB steps, and switch between AC/DC coupling at the input. I also added placeholder for capacitors, every place to able to handle the stability, if needed.

Now I just ordered the parts and the PCB for this power amplifier section. I still have a few addition in my head for this instrument, but I'll just build the amplifier itself, to check the performance. The other things come later:

  • Power supply for the analog parts (+-15V/300W)
  • Power supply for the digital parts (+5V, +12V), and fan controller for the cooling fans (Amp, Analog PSU)
  • TrueRMS converter, automatic range switch, ADC - for measuring voltage/current on the output
  • Control processor board
  • Front panel (LED display, buttons, rotary encoder, or just using a small TFT originally made for 3D printers)

Yes, maybe I overthink, overcomplicate things 😁

2022. augusztus 26., péntek

Rack mount power amplifier 1.

Another idiotic (never finished???) idea of mine.

As I go back to build audio equipment and bought enormous amount of old audio gear, I eagerly need something to test it in my lab. I started to build my test equipment into 19" racks (than disassembled everything. 😂)

For testing, I need a set of speakers, and a power amplifier.


  • Built into a 1U rackmount enclosure (I hate things on trays in the rack)
  • Use modul parts: Switching PSU, Class D amplifier board
  • Put all of the connectors to the front, to be easily accessible
  • Optional: back connectors with front/back switch


  • 500VA 24V PSU - $16.45
  • TPA3116 120W Class D board - $10.71
  • 1U Rack Chassis - $44.82 + $56.73 (Shipping)


No way.

Once more:

  • 500VA 24V PSU - $16.45
  • TPA3116 120W Class D board - $10.71
  • 1U Rack Chassis - $44.82 + $56.73 (Shipping)
Think a bit, look around.
Buy the chassis locally
  • 1U Rack Chassis - $50
No way.

Next iteration:
  • 500VA 24V PSU - $16.45
  • TPA3116 120W Class D board - $10.71
  • 1U Rack Chassis - $50
Look around more thoroughly:

I found quite a few outdated or broken 1U network switches. $12-$15 each

Much better.

The things arriving:

The Amp:

The PSU:

The Switch for repurpose:

My new A3 printer and sheet laminator is on the way to me. So the plan is to throw away the parts from one of the switches. build the connectors, volume pot on the front of the switch chassis or add some holding consoles (probably 3D printed) and design a new front panel, print laminate, cut and finally glue it with a double sided adhesive tape.
This is the plan. Looks super fast to me. Hopefully not another half baked, shelved project.

2022. augusztus 21., vasárnap

IC sorting, project idea?

In the last few days (rather weeks), I was playing with the ICs I have.

I want to have a kind of catalog on the things I "collected" during the last decades as electronics parts. Mostly on ICs. Actually I always have problem, when something pop out of my mind. I always look for new parts, instead of looking for my parts bins, what I already have.

I started to assemble an Excel list of ICs. There is already 432 rows in it and counting (not too much more, I guess could be additional 20-30 types in some project boxes). Hunting for datasheets, I think, that I'll be able to finish by end of next week.

During the inventory process I run into an interesting thing.

Probably you know about the family of digitally controlled analog switches (like CD4066). It has 4 analog switch in a single package.

What if, you have an IC containing 128 switches (organized in 8x16 matrix) in a single package, controlled digitally, even have separate negative supply, to allow the switched analog signal go bellow the ground? This thing is Mitel MT8816 (DIP-40 or PLCC-44 package).

If you have such thing, what would you build from it?

If you have lot of it, what would you build from it?

Actually I have altogether 172 (162 DIP, 10 PLCC) piece of it. I'm looking for project ideas. Yes, on the side of the obvious to build a 16 in 8 out audio crosspoint matrix for drive various amplifiers, tape recorders, etc.